pub struct AverageCollection {
    list: Vec<i32>,
    average: f64,
}
impl AverageCollection {
    pub fn add(&mut self, value: i32) {
        let result = self.list.pop();
        match result {
            Some(value) => {
                self.update_average();
                some(value)
            }
            None => None,
        }
    }
    pub fn average(&self) -> f64 {
        self.average
    }
    fn update_average(&mut self) {
        let total: i32 = self.list.iter().sum();
        self.average = total as f64 / self.list.len() as f64;
    }
}
fn main() {
    println!("Hello, world!");
}
